Production of benzene hexachloride



Feb. 23, 1960 FREDERICK E. KUNG ETAL PRODUCTION OF BENZENE HEXACHLORIDEFiled March 15, 1956 F'IGJ IN A A T u 0 OUT FIG. 2

INVENTOR. FRFGER/CK a .ealvoh #:wev c. smaw:

A TTORN! Y United States Patent PRODUCTION OF BENZENE HEXACHLORIDEFrederick E. Kung and Henry C. Stevens, Akron, Ohio, assignors toColumbia-Southern Chemical Corporation Application March 13, 1956,Serial No. 571,307

Claims. (Cl. 260-648) This invention relates to a novel method ofproviding benzene hexachloride compositions containing high gamma isomerconcentrations thereof. It relates to a novel method of selectivelyseparating isomers of benzene hexachloride. Moreover, it concerns anovel method whereby the gamma isomer of benzene hexachloride may beseparated from other isomers of benzene hexachloride.

The conventional methods of preparing benzene hexachloride described inthe literature involve the additive chlorination of benzene withelemental chlorine in the presence of an appropriate catalytic means,such as actinic irradiation. By recourse to the processes described inthe literature, it has been possible to manufacture benzene hexachloridecontaining a maximum of from about 12 to 16 percent by weight of thegamma isomer thereof. Frequently, the gamma isomer concentrations are aslow as 7 percent, orless, in the operation of such processes.

Additive chlorination of benzene in the preparation of benzenehexachloride results in the formation of at least five isomers thereof.These isomers have been designated as alpha, beta, gamma, delta, andepsilon. It has been universally recognized that the gamma isomer isuseful, notably in the insecticidal field. Although some uses have beensuggested for isomers other than the gamma isomer, it is the gammaisomer which appears to be of most commercial significance.

Because only a minor percentage of the benzene hexachloride produced inthe normal manufacture thereof is the gamma isomer, considerable importhas been attached to the development of various methods for separatingthe gamma isomer from the isomeric mixture. Preparation of compositionscontaining larger percentages of the gamma isomer of benzenehexachloride than'is provided by the chlorination of benzene has manyadvantages. It avoids the shipment of the insecticidally inert isomers.It makes it possible to formulate more concentrated preparations for usein the field by the farmer. It further allows for the recovery of theinsecticidally inert isomers so that they may be utilized, such as byconversion to other more useful compounds, not ably trichlorobenzen bydehydrohalog'enation of the benzene hexachloride. It also permits otherisomers to be concentrated and used for purposesother than insecticides,e.g., the delta isomer has been suggested to be a suitable herbicidalmaterial.

According to the present invention, it is possible to preparecompositions of benzene hexachloride which con- 2,926,198 Pa tented Feb.23, 1960 "ice containing low gamma concentrations of the delta isomer.Delta isomer contain more gamma isomer than is normally present inbencentrations on the order of percent or more by weight of benzenehexachloride are often attained by recourse to the instant invention. Inview of suggestions that the delta isomer has value as a herbicide, thepresent invention makes 'it possible to prepare valuable herbicidalcompositions.

It has been discovered according to this invention, that when-a mixtureof two or more isomers of benzene hexachloride is dissolved in a pair ofimmiscible solvents and the immiscible solvents are thereafterseparated, the solute in each solvent will contain a higher percentageof one of the isomers based on the total benzene hexachloride dissolvedin said solvent than the percentage of that isomer in the initialmixture. Thus, for example, if a mixture of gamma and delta isomerscontaining 50 percent by weight of'each isomer is dissolved in a pair ofimmiscible solvents and the solvents are then separated, one solventwill contain an isomeric mixture of benzene hexachlorides containingover 50 percent by weightof the gamma isomer based on the total benzenehexachloride present as solute therein. Likewise, the other solvent willcontain a solute having over 50 percent by weight of the delta isomer.

The above-described phenomenon is also observed when various isomericmixturesof benzene hexachloride are dissolved in a pair of immisciblesolvents. However, the exact distribution of each isomer in'each solventcomprising the pair of immiscible solvents depends on the particularsolvent pair and the relative volumes of the respective solvents. Thus,the prediction of which solvent will contain the solute enriched in oneor more isomers requires a knowledge of the particular solvent pair, andto a certain extent, the relative volumes in which each componentsolvent of the pair is utilized.

In this regard, it has been discovered that reference to thedistribution coefiicients of the various isomers in benzene hexachloridefor any given pair of immiscible solvents permits the judiciousselection of a suitable solvent system for selectively separating one ormore isomers from one or more other isomers. This distributioncoefiicient is defined as the concentration of a given isomer in theless polar phase divided by the concentration of that isomer in the morepolar phase for a given immiscible solvent pair when the isomer isdissolved in the solvent pair and the system is at equilibrium.Moreover, the constant is apparentlynot noticeably influenced by thepresence of other isomers in the system. Thus,-the coefficient may bedetermined by dissolving pure isomer in the immiscible solvent pair andanalyzing for the concentration of the isomer in the respective phases;such data is applicable in systems containing mixtures of isomersalthough it was obtained by employing the single isomer. The followingtable lists a series of illustrative solvent pairs and the respectivedistribution coefiicients for the major isomers, alpha, gamma, delta,and epsilon:

N Solvent pair Distribution coefliclent (k) Non-polar Polar a 7 A cBenzene 16. 7 13. 3 5. 5 13.0 Perchloroethylene. 12. 8 7. 9 0. 9 1. 5Ethylene dlchloride 5. 1 5. 1. 2 2. 4 Carbon tetrachloride- 8. 6 6. O 0.6 1. 6 Methyl chloroform. 12. 0 8. 4 1. 2 2. 1 Methyl iodide- 13. 2 13.3 3.0 5. 5 Ethyl other- 8. 4. 5. 2 2. 5 2. 3 n-Hexane (comm) 3. 0 1. 90.26 0.30 Pentnne 3.0 1. 1 0.10 0.18

7. 1 3. 7 0.8 1. 2 Methylcellosolvon 0. 42 0. 29 0. 17 O. 10Butanediol-1,3 1. 7 1. 5 0. 17 0. 27 PolyglycoHOO. 0. 2' 0. 14 0. 009 0.031 Formamide. 11.5 6. 6 2. 0 3. 4 o 30 17. 5 l1. 1 16. 7

Ethylene glycol. 2. 3 1. 46 0. 15 0.29 0--- 3.4 2.4 0.22 0.35Polyglycol-400. 0.5 0. 3 0. 036 0. 063 Diethylene glycol. 0. 41 0. 17 0.0145 0. 006 Cyclohexane do 0.61 0. 27 0. 032 0. 043 Carbon tetrachloridedo 0.70 0. 42 0.046 0. 14 Perehlorocthv ..-...do. 1. 75 0.9 0.09 0. 12Trlchloroethylene Ethylene glycol 15. 6 10. 3 1.08 1. 7 o 3. 4 3. 6 1. 43. 3

2.0 1. 14 0. 096 0. 10 Trimethylene glyc 2. 7 1. 35 O. 18 0. 26

Acetonltrile 2. 8 0. 17 0.082 0. 064

The magnitude of the distribution coefiicients for each isomer for agiven solvent pair also reflects the relative solubility of each isomerin the respective phases of the particular immiscible solvent pair. Bychoosing suitable solvent volumes, it is possible to provide a systemwhere- .in the selective separation of one or more isomers from one ormore isomers is at an optimum for a particular solvent pair.

For example, the distribution coeflicients for ethylene glycol-pentaneare:

k =3.0 k.,=l.1 kA=0.l0 k.=0.18

Varying the ratio of the volumes of pentane and ethylene glycol willpermit the attainment of varying degrees of resolution. The followingexample is intended to illustrate the value of this data. Assuming anisomeric mix 'ture of 100 grams, containing the four isomers in equalproportions and equal volumes of solvent, the following mixture willcomprise the solute in the pentane.

Concentration alpha in pentane Concentration alpha in ethylene glyool Ifa=grams alpha in pentane, -a=grams alpha in ethylene glycol. Then bysubstitution:

may be predicted to be 49.5 percent by weight of the solute.

If the volume of pentane is only one-half that of ethylene glycol, allother conditions being the same, the following calculations may be made:

Weight alpha in pentane volume of pentane weight alpha in ethyleneglycol volume of ethylene glycol However, volume of pentane is equal toone-half volume of ethylene glycol. Thus,

. (y) weight alpha in pentane 2 weight alpha in ethylene glycol Byfollowing these calculations, the respective amounts of the isomers inthe solute of the pentane phase may be anticipated as:

a=15 grams -y=8.95 grams A=l.19 grams =2.06 grams This represents analpha concentration of 55 percent by weight of the solute in thepentane.

Accordingly, the present invention may be practiced by dissolving anisomeric mixture of benzene hexachloride containing all the knownisomers thereof into a pair of immiscible solvents and separatingrespective liquid phases thus formed.

Usually, the dissolved benzene hexachloride present in each of theseparated phases is recovered by known expedients, notably distillation,crystallization, etc. with the solvent being collected and reused. Undercertain circumstances, the phases need not be subjected to furthertreatment, but may be suitable for direct use as a liquid formulation.Normally, however, it is more economical to separate the solvents andbenzene hexachloride.

Although the description of this invention will be made with specificreference to providing compositions containing enhanced gamma isomerconcentrations, e.g., the selective separation of the gamma isomer fromother isomers, it should be understood that the process may be utilizedto separate or concentrate any given isomer of benzene hexachloride withrespect to a mixture of any two or more isomers.

A specific embodiment of this invention comprises introducing a mixtureof at least alpha, gamma, and delta isomers into a pair of immisciblesolvents and recovering the benzene hexachloride present in the lesspolar solvent, notably the alpha and gamma isomers.

Another embodiment of the present invention involves introducing amixture of isomers containing alpha and gamma isomers, butnot-containing any appreciable per' centage of delta isomer, andrecovering the benzene hexachloride in each solvent to separate thealpha and gamma isomers from one another. This embodiment is ofparticuselectively distributing in the more polar solvent. 'more polarsolvent comprising the fresh polar solvent lar utility because many ofthe solvent pairs readily permit a separation of the delta isomer fromthe alpha and gamma isomers, but with the delta isomer presentsatisfactory separation of the alpha and gamma isomers is diflicult oreconomically unattractive in the same separation. It will be understoodthat this particular embodiment may have particular utility incombination with a process wherein the delta isomer is removed from thealpha and gamma isomers and a second step is utilized to separate gammaand alpha isomer. Such process, for example, would comprise treating theless polar solvent phase which contains essentially no delta isomerobtained from a prior separation with a fresh polar solvent to separatethe alpha and gamma isomers, the gamma isomler T e may be even the samesolvent employed in the delta separation so long as it has been freed ofdelta isomer. It may be a diflerent solvent (different chemicalstructure) entirely.

Thus, separation of gamma and alpha isomers is most aptly conducted inthe absence of an appreciable percentage of delta isomer according tothe invention. Some variation in the amount of delta that may be presentis,

however, permissible since the gamma and alpha separa- *tion ispossible, although pronouncedly more difficult even with delta present.

should contain a minimum concentration of the delta isomer, below 4percent, and when practical the mixture should be essentially free ofdelta isomer.

Any expedient for selectively removing the delta isomer is useful.According to one embodiment hereof, this removal may be achieved by theherein described process of dissolving a benzene hexachloride mixtureincluding the gamma, delta and alpha isomers in a pair of immisciblesolvents for benzene hexachloride, forming two liquid phases, the lesspolar solvent predominating in one phase and the more polar solvent inthe other phase, and selectively distributing the gamma and alpha isomerin the less polar phase. The delta isomer distributes selectively in themore polar phase.

Practice of this invention is predicated upon employing a pair ofimmiscible solvents." By pair, it is to be understood that two or morecomponents is meant, as will hereinafter be explained.

It has been found that a suitable pair of immiscible solvents comprisesone or more polar and non-polar solvents. In this regard, polarity is arelative term and the system may be characterized as containing a morepolar and less polar solvent. As a practical matter, immiscible solventsnormally differ in dielectric constant by at least about to or more.Thus, by stipulating that the solvents are immiscible usually inherentlydefines solvents which have substantially different polarities.Moreover, immiscible solvent pairs are generally comprised by anon-polar solvent and polar solvent. For the purposes of explaining theinvention, the terms polar and nonpolar solvent will be employed,although it is to be under- I stood that such expression will refer tothe relative polarhave density differences at atmospheric conditions,e.g.

room temperature, are most suitable. In some instances,

-fies the hereinbefore-described requirements.

it may be possible to employ solvents which have difierent densitiesonly within a specific temperature range by effecting the separation ofthe solvents within such range.

Manifestly, the solvents employed should be chemically inert under theconditions at which the invention is practiced. That is, they should notreact with each other, benzene hexachloride or any other material thatmay be present in the system to produce a compound or compounds notoriginally present. Under certain special circumstances wherein a newmaterial is produced that has marketable value, chemical reaction may bepermissible. Even then, if considerable chemical reaction isencountered, it is preferable to select conditions and solvents whichavoid or minimize such reaction.

The instant invention makes it possible to selectively separate oneisomer from other isomers. The degree to which the selective separationis accomplished, and also the isomers which may be separated depend onthe particular solvent pair that is utilized. Thus, the particularobjective of the separation governs to some extent the solvent pairwhich is employed, alhough beneficial results will accrue from the useof any solvent pair which satis- Optimum results for a specificseparation are, therefore, obtained by recourse to selected solventpairs.

The efiiciency of a particular solvent pair in providing the desiredobjective, to wit, the ease with which the resolution of certainmixtures of isomers into its component isomers or into mixtures whichcontain larger amounts of one isomer than the initial mixture, may bepredicted by reference to the separation coefficient of the solventpair. This separation coefitcient is not always the same value forseparation of diiferent isomers. Thus, one solvent pair often willprovide an easier separation of the gamma and delta isomers, whereasanother solvent pair will provide a more eflicient separation of thegamma and alpha isomers. However, it is emphasized that any immisciblesolvent pair which otherwise fulfills the outlined requisites willprovide a beneficial separation.

As has been indicated, the separation coefiicient of any solvent pairmay vary depending on the isomer separation involved. The separationcoeflicient of a solvent pair for any two isomers of benzenehexachloride is defined as:

(W2) (W?) (W2) (W2) wherein W represents the weight of isomer x insolvent A, W the weight of isomer in solvent B, W the weight of isomer yin solvent A and W the weight of isomer x in solvent B. A coefficient of1 indicates no separation whereas the greater the difference of thevalue for K from 1, the easier the separation of x and y may be expectedto be. Thus, small coefiicients, e.g., less than 0.8 or coefficientslarger than about 1.2 indicate suitable solvent system. This coefiicientis indicative of the maximum effectiveness of the solvent pair inresolving a mixture containing x and y into separate components at andy.

The separation coefficient K as defined above, it will be appreciated,also represents the ratio of the distribution ccefiicients of the twoisomers in question. Thus, K in the above equation is equal to E ky Inthis regard, it may be mentioned that the coeflicient is indicative ofthe number of steps or stages that may be required to provide a completeor essentially complete separation of x and y. With a comparativelysmall coefficient, say of about 1.5 to 3, a considerable number of stepsor stages are indicated. As the coefiicient increases, the number ofthese steps or stages should decrease.

This coetficient for a giventemperature may be ascerglycols are foundmost suitable. ethanol, isopropanol solutions are of particularimportethylene glycol;

tainedbydissolving given amounts of x and y isomers 'in the selectedsolvent pair intimately mixing the pair ito achieve equilibrium, andthereafter analyzing the x andy isomer content in one or both of theresulting phases at the temperature.

Some of the polar solvents which may be employed to *comprise the morepolar solvent in the solvent pair used to perform the instant inventioninclude normally liquid and higher polyethylene glycols, glycol ethers,acetonitrile, formamide, formic acid, aniline, and various othercompounds including methyl Cellosolve, ethylene carbonate, nitromethane,and methyl Carbitols. In general,

materials in which benzene hexachloride will dissolve and which have adielectric constant of above about i aresuitable.

The polar solvent portion of the solvent system contemplated by thisinvention are not limited to the use of any one of the above-enumeratedsolvents, but may constitute a plurality of such solvents so long asthey are completely miscible. In this regard, aqueous solutions of thewater-soluble solvents recited are also useful. Mainly, aqueoussolutions of the aliphatic alcohols and Aqueous methanol,

ance for reasons that will become apparent.

Solvents which are suitable for providing the non-polar (less polar)solvent for the immiscible solvent pair employed in the practice of thisinvention include the normally liquid aliphatic and cycloaliphatichydrocarbons,

dimethyl cyclohexane; benzene, decalin, indane, Skellysolves, petroleumfractions, and the like. Halogenated hydrocarbons, and notablychlorinated hydrocarbons,

which are normally liquid, such as carbon tetrachloride, "chloroform,methyl chloroform, ethylene dichloride, tri- I chloroethylene, -methylchloride, methyl iodide, hexachlorobutadiene, hextetrachloroethane,perchloroethylene,

achlorocyclopentadiene, and the like are also suitable. Generally,halogenated hydrocarbons containing up to and including four carbonatoms are satisfactory. Ethers, such as ethyl ether are also useful. Theinvention, however, is not limited to the use of but one of thesenonpolar solvents to comprise the non-polar phase of the solvent pair.Mixtures of miscible non-polar solvents are contemplated, subject to thelimitation that in admixture with the polar solvent, they provide asolvent pair having the requisite immiscibility and other physicalproperties.

In the event recourse to multi-component polar and non-polar phase, e.g.when two or more solvents are employed to provide either one or both ofthe respective phases, it is necessary to consider certain factors toinsure'satisfactory performance of the invention. Notably, themiscibilityof the various members of one phase must be such that, duringthe course of carrying out the invention, there is no tendency for morethan two phases to be formed. Thus, the possibility that one of theseveral solvents may disrupt the normal miscibility (or immiscibility)of the system, particularly in a multi-step process, should beconsidered. However, such situations are the exception rather than therule.

Typical solvent pairs which are used in the instant in- .vention includeamong others cyclohexane-ethylene glycol; perchloroethylene-ethyleneglycol; ethylene dichloride-ethylene glycol; carbontetrachloride-diethylene glycol; cyclohexane-diethylene glycol;perchloroethylene-dimethyl chloroform-ethylene glycol;methanol-cyclohexane; benzene-ethylene glycol; methyl iodide ethyleneglycol; ethylene glycol-carbon tetrachloride, ethylether-ethyleneglycol; aqueous methanol 'cyclo hexane; nitromethane-n-hexane; ethyleneglycol-pentane, ethylene glycol-cyclohexene; cyclohexane-methylCellosolve; cyclohexane-butanediol-l,3; cyclohexane-polyethylene glycol(polyglycol 400--Union Carbide and Carbon); chloroform formamide.

Some of these solvent pairs are especiallysuitable for separatingspecific pairs of isomers. Thus, ethylene glycol-carbon tetrachloride;diethylene glycol-carbon tetrachloride; diethylene glycol-pentane;diethylene glycolperchloro-ethylene; pentane-ethylene glycol; andcyclohexane-polyethylene glycol apparently provide the highestseparation coefiicient for the gamma-delta isomers and normally offer anoptimum solvent system for separating the gamma and delta isomers.Similarly, perchloraethylene-ethylene glycol; pentane-ethylene glycol;carbon tetrachloride-diethylene glycol; pentane-diethylene glycol;cyclohexane-polyethylene glycol; chloroform-formamide; decalin-ethyleneglycol appear to be the more suitable pairs for separating the gamma andalpha isomers.

his not intended that the inference should be drawn that because asolvent pair is eminently suited for separation-of a given pair ofisomers that it is not suitable for separating other groups of isomers.On the contrary, it may be noted that cyclohexam-polyethyleneglycolappears to be among those classified as suitable for resolution ofgamma-delta and gamma-alpha. It appears taht all solvent pairspossessing the requisite physical characteristics provide a desirableresult, with some being more suitable for a specific task.

Various expedients may be employed to effectively practice the processof this invention. They all, however, perform certain basic steps whichcomprise dissolving the isomer mixture of benzene hexachloride in asolvent pair having the aforedescribed characteristics, and thereafterseparating the immiscible phases of the resulting mixture. Normally, therespective phases, after being separated are subjected to separatefurther treatment to recover the solute therein, namely, the benzenehexachloride, as by distillation, precipitation or equivalent operation.

The temperature of the system, e.g. the solvent pair, at which theinvention is performed may be widely varied. It is preferable to performthe invention at convenient temperatures, e.g. about 25 C. It does notappear that the temperature is critical. Since many of the solvents arerelatively volatile, the lower temperatures are favored. However, aslong as the temperature provides the liquid solvent system (does notpermit the formation of a solid phase due to freezing) and does notvolatilize any solvent appreciably, it is suitable. Temperatures fromabout 0 C. to about C. generally satisfy these requirements. Attemperatures of between 15 C. and 40 C., the process appears to operateat or near optimum overall efliciency.

Generally, each solvent comprising the pair should be present in atleast sufiicient quantities to dissolve the respective portion of thebenzene hexachloride feed which is expected to selectively dissolvetherein. It will be recognized that such quantities will varydepending'on the temperature, since solubility of benzene hexachloridesin these solvents increases with higher temperatures. At highertemperature less volume of solvent will normally be required to performthe same job.

In many instances, one such contact with the solvent pair, as outlinedabove, does not provide as complete a separation of isomers as may bedesired. Accordingly, it is often advantageous to repeat such stepsemploying the respective phase to form one of the phase in the nextoperation. For example, the polar phase containing the selectivelydissolved mixture of isomers may be treated with a fresh non-polarsolvent to further selectively concentrate one or more isomers in thepolar solvent. In a similar fashion, the non-polar phase may be admixedwith a fresh polar solvent.

- One of the operations which embodies this procedure is apseudo-countercurrent batch process. In such process, a plurality ofmixing chambers and settling chambers are provided. Benzene hexachloride(isomeric mixture) is added to one such mixing chamber as a feed. Thesame procedure is followed in each pair of chambers comprising a mixingand settling chamber. The nonpolar and polar solvents are mixed,preferably vigorously, and then separated by settling and decanting. Onephase is then moved to the next adjacent pair of chambers, while theother phase is moved in an opposite direction to the other adjacent pairof chambers.

Fresh solvents are introduced suitably at each end of the line of pairsof chambers, the non-polar solvent from a different end than the polarsolvent. Similarly, the isomeric mixture of benzene hexachloride to befractionated is added at one stage, usually an intermediate stage. Theproduct, that is, solvent plus benzene hexachloride, is ultimatelyremoved at the respective ends of the line. Removal of the non-polarsolvent containing the selectively removed benzene hexachloride takesplace normally at the end of the line of chambers wherein the freshpolar solvent is introduced into the system.

Quite a variety of apparatus may be used to provide a means forproviding a continuous countercurrent process. Generally, apparatus suchas towers which have alternating agitating and settling zones wherebythe re sults achieved in the settling and mixing chambers are simulatedmay be used. One such tower, for example, provides alternating zones,one set of such zones having an agitating means therein While the otherset of zones serves as a settling area and is not subjected toagitation. Another provides packed zones to achieve a suitable alternateset of settling areas to operate conjunctly with the agitating zones.

Other such equipment for accomplishing results similar to this will beapparent to those familiar therewith, including baflied towers, andtowers packed with inert materials such as Raschig rings and Berlsaddles. Often a means for jetting one of the solvents down throughvarious portions of the tower is utilized.

These towers are operable in a multitude of ways which depend, to amajor extent, on the objective of the selective separation. Incountercurrent operation, the heavier solvent is fed into or adjacentthe top of the tower and the lighter solvent enters the tower at itslower portion. By virtue of ther respective densities, downward andupward flow of the solvents occurs and the lighter solvent is withdrawnfrom the upper portion of the tower; the heavier solvent is removed fromthe lower section.

The isomeric mixture of benzene hexachloride (feed I benzenehexachloride) may be introduced into the tower at any point. In one typeof operation, the feed ben zene hexachloride is introduced at one end ofthe tower. In another, it is introduced intermediate the extremities ofthe tower.

When the benzene hexachloride is introduced into the tower at one endthereof, it may be conveniently dissolved in the solvent that isintroduced at that end. Thus, one feed stream to the tower may contain asolution of the benzene hexachloride. Since benzene hexachloride isnormally solid, this avoids difficulties attendant to the introductionof a solid into a liquid system.

If benzene hexachloride is introduced into the tower intermediate thefeed points of the solvents, the problem of addition is somewhat morecomplicated. It may be advisable to introduce molten benzenehexachloride. Alternatively or in conjunction with molten feed, the feedof benzene hexachloride may be facilitated by dissolving it in a smallquantity of one of the solvents. Generally, the volume of solvent addedto the system in this manner should be kept at a minimum; forsatisfactory perform- .ance of the tower the solvent introduced thuslyshould be less than 25 percent of the total amount of that solvent addedto the system.

Still another expedient is available to enhance the efiiciency of thetower. The material issuing out of any given end of the tower may bepartially recycled to the tower at a point above or below the respectiveend, as the case may be. For example, the heavier solution which iswithdrawn from the lowermost point of the tower may be recycled to ahigher point in the tower than the point of withdrawal. The recycledmaterial may comprise a'portion, but not all, of the withdrawn solution,with or without partial or total removal of the solvent. Similarly, itis possible to recycle a portion of the lighter solution leaving theupper section of the tower to a point below its removal point, with orwithout partial or complete removal of the solvent.

The towers herein described and their equivalents may be used incombination with one another depending again on the particular ends tobe accomplished. One convenient combination of towers utilizes at leastthree towers. The solvents issuing out of the respective ends of thefirst tower provide one solvent feed for each of the other two towers.Fresh solvent is employed as the other feed in each of these two towers.Other combinations of towers and feeds will be apparent to oneacquainted with the use of such extraction equipment.

Ultimately, whether one or more towers are employed, the respectivestreams emerging from the final step are treated to recover thesolvents, which recovered solvents are conveniently reintroduced to thesystem as fresh feed. Thus, the stream emerging from one end of thetower may be subjected to distillation with the distillate beingappropriately cooled and returned to the tower. The residue from suchdistillation will be benzene hexachloride having an enhancedconcentration of at least one isomer thereof as compared with thebenzene hexachloride feed.

Instead of recourse to a distillation step, comparable expedients may beemployed. The solute may be precipitated by cooling the solution, byaddition of a liquid which is miscible with the solvent to provide asolution in which the solute is less soluble, partial distillation ofthe solvent followed by cooling to precipitate a solid phase, or thelike. Thereafter, filtration, centrifugation, settling and decanting, orother means for separating solid and liquid phases may be utilized.

Instead of relying on gravity to cause the two solvents to rise or fallin a tower, it is possible to use centrifugal force to provide theintimate contact between the two solvents. Thus, the instant inventionmay be practiced by recourse to a Pobielniak centrifugal extractor, orother such apparatus. In such extractions, the heavier solvent is fedinto the center of a cylindrical chamber and by rotating the chambercentrifugal force causes the heavier solvent to move to the outermostportion of the chamber. The lighter solvent is fed under pressure at theoutermost portion of the chamber and effectively moves toward the centerthereof. Thus, the outward movement of the heavier solvent coupled withthe inward movement of the lighter solvent, due to rotation of thechamber causes the respective solvents comprising the solvent pair tomove in countercurrent flow.

A plurality of extractors which utilize centrifugal force to perform theextraction in such manner are known. They all are basically the same.Some, however, employ mechanical expedients to increase the efliciencyof the extraction, notably, by increasing the flow paths of therespective solvents. This provides longer contact between the solvents.All sorts of bafiie arrangements, perforated baffles, etc. are used toenhance the operation of centrifugal extractors.

In these extractors (towers or centrifugal extractors), benzenehexachloride feed may be accomplished by dissolving the isomeric mixturein one of the respective solvents which is introduced into the column.Under certain circumstances, it is also possible to add the benzenehexa- -chloride asa-molten mass to the extractor, provided precautionsare taken to minimize -or avoid clogging due to solidification. Often,heating means may be employed to maintain the feed molten until it hasentered the extractor and has been dissolved. Sometimes it may bedesirable to add a small portion of one solvent to the feedto enhenceits flow and dissolving in the extractor.

Essentially all isomeric mixtures of benzene hexachloride may be treatedin accordance with this invention with beneficial results. Certainmixtures, however, are most usually encountered in the commercialmanufacture of benzene hexachloride and such isomeric mixtures are theones which may be expected to be employed in practice of the instantinvention. One such mixture is the benzene additive chlorination productprepared by reaction of benzene and chlorine in the presence of anappropriate catalytic means, notably actinic irradiation. The exactisomer distribution in this product varies somewhat, depending on theexact process employed. A typical range of the relative amounts of therespective isomers is:

Alpha=50-70 Beta=5-10 Gamma: 12-16 Delta: -15 Epsilon=2-5 Isomericmixture prepared by additive chlorination mixtures wherein othercatalytic means besides actinic light is employed suchas'organicperoxides are also useful. Similarly, the additivechlorination product prepared in accordance with the process describedin application, Serial No. 225,854, filed May 11, 1951, in the names ofJoseph A. Neubauer, Franklin Strain, and Frederick E. Kung now abandonedin favor of US. Letters Patent 2,717,238, granted September 6, 1955, maybe used.

Another isomeric mixture that is frequently encountered in thecommercial manufacture of benzene hexachloride is one that results fromthe filtration of the additive chlorination slurry and recovery of thesoluble isomers. This isomeric mixture maylikewise be employed in thepresent vprocess. US. Patent No. 2,569,677, granted October 2, 1951,describes one typical method of obtaining such isomeric mixture. Otherprocesses which provide somewhat better separation of the alpha isomerthan the one described in the aforedesignated patent may also be used toprovide an isomeric mixture which is suitable for carrying out thepresent invention.

The present invention has also been 'found to have particular utilitywhen employed in cooperation Withother techniques for resolving isomericbenzene hexachloride mixtures into its components, and notably providingessentially pure gamma isomer, e.g. lindane. One technique for obtaininglindane involves the extraction of solid benzene hexachloride containingfrom 12 to 55 percent by weight of the gamma isomer with a loweraliphatic alcohol, notably methanol or ethanol. The resulting extract,containing an enriched gamma isomer content is thereafter selectivelyprecipitated by addition of water to the extract or by cooling theextract. A pure gamma isomer precipitate may be obtained in this manner,or alternatively, a product containing upwardsof 70 percent of the gammaisomer may be prepared.

Unfortunately, theprocess outline in the preceding paragraph has certainlimitations, namely, that the higher the gamma isomer concentration isin the precipitate, the less efiicient the process. This is, if lindane(99 percent or more gamma) is precipitated, a substantial portion of thetotal amount of gamma isomer remains unprecipitated. Being satisfied toproduce a less concentrated gamma product as the precipitate decreasesthe amount of-gamma that remains in solution, but it is economicallyimpossible to waste the soluble gamma isomer since it still represents aconsiderable portion of the total amount that istreated.

'Attempts to ree'ycle the contents of the aqueous methanol solution,such-that recovery of the unprecipitated gamma isomer is etfected, havebeen relatively unsuccessful. It seems that a considerable amount ofdelta isomer builds up by such recycling and eventually makes theprocesses inefficient and often unsuccessful.

However, in accordance with this invention, it is possible toselectively separate the gamma and delta isomers present in an aqueousmethanol solution. It has been found that by' extracting the aqueousmethanol solution with a non-polar solvent such as hexane or othershereinbefore enumerated, the delta isomer tends to concentrate in thesolute of the polar material whereas the gamma isomer remainspredominately in the non-polar phase. By recourse to the presentinvention, it is, therefore, possible to treat the aqueous methanolsolution to recover the gamma isomer present therein whilesimultaneously effecting a separation of the troublesome delta isomerfrom the gamma isomer.

Thus, when this invention is practiced in cooperation with theaforedescribed process for preparing lindane or other high gamma isomercontaining products, no interference in the continuous operation of suchprocess is encountered due to a build-up in delta isomer concentrations.Moreover, the instant invention increases the efiiciency of suchprocesses by permitting the unprecipitated gamma isomer to be recoveredand, if desired, to be recycled for further treatment in the process.

The following examples illustrate the instant invention:

Example I The apparatus used in this example comprised fiveSOC-milliliter flasks individually fitted with agitators and drainplugs. Reference to Figure 1 of the drawings will illustratediagrammatically how the five flasks were disposed relative to oneanother.

At the outset, each flask was charged with 200 milliliters of ethyleneglycol, 50 milliliters of carbon tetrachloride, and 5 grams of benzenehexachloride. This benzene hexachloride analyzed as follows:

Each flasks contents was thereupon stirred for one-half hour at roomtemperature (e.g. 25 C.). The phases therein were then drained intoseparate vessels and reintroduced into extractors so that the glycolphase moved one extractor to the right and the carbon tetrachloridephase moved one extractor to the left. In the drawing, A representsethylene glycol and B designates carbon tetrachloride. New solvent wasadded at extractors 1 and 5: fresh glycol (200 milliliters) was added at1 and fresh carbon tetrachloride (50 milliliters) was introduced at 5.Benzene hexachloride of the same composition was added at extractor 3.Stirring for 30 minutes followed by separation of the phases plusmovement of the phases to the respective adjacent extractor waseffected. Fresh additions to the system was made in the manner alreadydescribed. Each addition of the two solvents and benzene hexachlorideconstituted a separation-addition step. The terminal efiluents areremoved from the system.

This procedure was repeated until ten (10 separationaddition steps wereperformed. The ethylene glycol phase removed from extractor 5 and thecarbon tetrachloride phase emanating from extractor 1 were then treatedto remove the benzene hexachloride solutiou "apparent.

-'"therein*and submitted to infra-red spectroanalysis to determine theisomer distribution. 1

Benzene hexachloride, grams Isomeranal sis ercent Phase Y ID Alpha BetaGamma Delta Epsilon OUIO menu

isomer, 30.0 percent.

Example 11 Using the same apparatus as described in Example I andfollowing essentially the same procedure, the effect of usingn-hexane(commercial grade) and 90 percent 'methanol (balance water) as thesolvents was investigated. In this case, 200 milliliters of n-hexane,100milliliters of 90 percent methanol, and 10.0 grams of benzenehexachloride were employed. The procedure in this example dilfered fromExample I in that the benzene hexachloride was fed at extractor 5 in amethanol solution, e.g., terminal feed as distinguished fromintermediate feed was employed.

The following are the analyses of the respective benzene hexachloridecompositions:

Benzene Isomer distribution, percent Phase n-Hexane.. Methanol- Feed NCOThe large difference in the contents of the respective phase withrespect to the gamma and delta isomers is The delta isomer tends toaccumulate in the methanol phase and a product containing 59.5 percentdelta isomer was attained. Conversely, a gamma isomer content of 48.5percent was achieved in the hexane phase. By continuing the extractionemploying more than extractions, even greater resolution of the isomersmay 'be achieved.

Example 111 In order to demonstrate the applicability of the presentprocess to commercial liquid-liquid extraction of the isomers, thefollowing process was performed in a Scheibel ,column.

Reference to Figure 2 of the drawings will permit more completedescription of the column employed. It

. included glass tube 4 which was four feet high and had 14 of a"settling zone" 6 and an agitating zone7. Each settling zone wasprovided by loose metallic mesh '8 which filled the entire diameter ofthe tube and was approximately three inches deep. The agitating zone wasprovided by a zone about V2 inch deep wherein agitator 9 was disposed.

Agitator 9 consisted of a four-finned element anchored to shaft 3..Figure 3 which is a cross section taken at AA of Figure 2 of thedrawings depicts the configuration of this element and fins 10.

For end feed, the heavier solvent is introduced via tube 12 into theuppermost settling zone while the lighter solvent is charged via tube 13into the lowermost settling zone. The heavier solvent is withdrawn fromthe tower through tube 14 while the lighter solvent leaves the system byway of tube 15. The feeds are pumped by appropriate means (notillustrated) into the column while the streams emanating from the columnare collected in suitable storage vessels (not shown).

In this experiment, the column was operated with the heavier solventcomprising the continuous phase throughout the entire length of thecolumn. This was achieved by regulating the highest point of inverted U16 which was adjustably connected to take-0E tube 14 through a rubbertube element.

An aqueous methanol solution containing percent by volume of methanolwas fed via tube 12 to the highest settling zone. This solutioncontained 8 grams of benzene hexachloride per milliliters thereof andwas introduced at the rate of 308 milliliters per hour. The benzenehexachloride in solution had an isomer distribution as follows asdetermined by infra-red spectroanalysis:

Alpha: 16.1 Beta: 4.9 Gamma: 17.6 Delta:40.2 Epsilon: 12.1

v The other solvent employed was n-hexane (commercial grade comprising70 percent n-hexane and the balance other hexane isomers) and it wasintroduced into the system via tube 13 at the rate of 222 millilitersper hour.

With the feeds being introduced as described, drive means 5 was operatedat 900 revolutions per minute to rotate agitator element 9. Theoperation was performed at room temperature, 25 C.:3 C.

After the column had been in operation for three hours, samples of eachphase leaving the column were treated to recover the residual benzenehexachloride therein by distillation of the solvents. The respectivecompositions were subjected to an infra-red spectroanalys'is toascertain their isomer distribution. Thereafter, during the course ofthe run, samples were taken periodically and analyzed.

The residual benzene hexachloride in the methanolic liquor leaving thetower, when recovered from the solvent, was a tan, crystalline material.It was extremely rich in delta isomer. The product recovered from thehexane stream emanating from the column was an oily mass whichcrystallized slowly on standing at room temperature.

The feed containing the benzene hexachloride in this example wasobtained by taking the additive chlorination product prepared by addingelemental chlorine to benzene which is irradiated with actinic light andremoving the solid phase that forms during the reaction. Thereafter, thebenzene hexachloride (700 grams) recovered from the liquid phase wasextracted with 2600 grams of methanol leaving behind a cake. To thefiltrate Was first added 520 grams of alcohol and then 700 grams ofwater. With the addition of water and cooling, a precipitate forms. Theaqueous methanol separated from this precipitate constituted the aqueousmethanol feed for this experiment.

The 't'oIIoWing-table lists thevarious yproductsof Zthe Theifollowingtable summarizes-the variable operating overall procedure of thisexample: cofldlflons and results:

Relative Ben volumes W Benzene hexachloridelsomer analysis zene Percentisomer distribution (milliliters) @3535 Source 15011a;i

c on 9 A ueous na B Y A l weight, mP l'hflflfll Hexane grams a B 1 v A e66. K1 :5 1. Additive chlorination 135 'ifi' 13.8 33.3 21.2 15.0 producti s aloha iii 4.4 2.0 4.5 10.0 08.0 125 cgkeformed durmg c 104 7.7 15.03.0 33.0 21.0 13.0 nnatlon 700 21. 0 2. 0 42. 5 20. 0 0 140 3 4 0 6. 54. 5 73. 0 l2. 5 I Isomer weight (grams)- 147 14 298 144 56 i5; 6 16. 04.0 32. 0 23.0 '10. 0 2. Cake 151; after methanol ii' 3.1 0 5.5 3.0 77.012.5 extract1on. 62 64.0 0 '28.5 1-0 ifi' 8 ,9 18.0 2.6 -32.0 22.8 10.7

Isomer weight (grams). 0 18 1 1 .15 i a' Analysis 8 grams $lZ%ii-t-2lifttli benzene l l 11 m anolsolufion U5 0 7&0 0 v2.0 perl00m1ll1llt0rS)394) 4 A Isomer wetilght (1gran11s) 275 48 0 209 0 6 queens me ano so u-I on after removing efi l 2315 stlge tower per given unit of time.Volumes are those of the Feed to column 360 16. 1 4.9 17. 6 40. 2 Y 12.1 2o Isomer weight (grams)- .58 18 63 145 44 Example V 5. Aqueousmethanol stream 1 Him tower h t 144 1. g 5.1; 5. 7%; 12. In this seriesof 6Xpt3l'lmHl.S,"th6'CECCUVCDESS of'cyclosomer wei ams 6. Hexane streamfrom tower. 216 22.5 .3.5 23.0 23.0 10.5 Pexane and ethylene glygol as asolver m separatlsomerwelrht (s 49 8 50 23 mg gamma and delta isomerswas investigated. The

25 procedure consisted of dissolving 5 grams of delta isomer and 5 gramsof gamma isomer in a mixture of the cyclo- Reference to items 5 and 6 inthe table makes it evident hexane-ethylene glycol solvent system,agitating 'the. two

that resolution of the delta and gamma isomers may be solutions,separating .the phases, .recoveringthc solute achieved by recourse tothe instant invention. The process ineach separated phase and analyzingby. 1nfra-red.spec including the methanol extraction, precipitation, andtroanalysis the respecuve products for isomer .d1str1buliquid-liquidextraction provides a commercially feasible tion. process for recoveringhigh gamma isomer containing vAs will be clear from the followmgtablqtheeffect products without undue waste of a significant portion of ofvarying the volume of solvent, temperature and ratio of the total gammaisomer involved. of volumes was considered in these-experiments:

Products-Analysts Volumes, mllllllters Tgnp Cyclohexane phase Glycolphase C5H1: CgHgO, Weight 7 A Weight A (grams) (percent) (percent)(grams) (percent) (percent) 100 100 1 Room 4.0 81.0 21.0 4.9 27.0 59.5400 400 Room 4.0 78.5 18.0 5.2 25.5 70.5 1, 200 1, 200 1 Room 4.5 75. 020. 5 5. 0 24. 0 74; 0 400 400 7 3.0 81.0 15.5 5.7 27.5 73.5 400 400 254. 0 78. 5 1s. 0 5. 2 25. 5 70. 5 400 400 70 5.8 04. 5 30. 0 a. 9 23. 572.0 25 '25 70 5. 5 03. 0 a5. 5 a. 2 24. 5 74. 5 200 400 1 Room a. 2 s3.5 15.0 0. 3 32.0 04.5 600 200 1 Room 6. 5 05. 5 s2. 5 3. 2 '17. 5 81.6

As was explained previously, the separation of the This data make it.clear that evenin=a.-'single-stage exdelta and gamma isomers, notablyfrom the extract (item traction, at least partial resolution ofagamma-delta 4 in the table), made it commercially u i bl {0 Drag.isomer mixture indicates that considerable latitude 1n temtice a processfor preparing lindane or other high gamma Peratllre, Volumes of Solvent,and ratio of the V0111!!! isomer products by addition of water to analcoholic exof tha Solvent is Permissibletract. With the presentliquid-liquid extraction, this problem is overcome. Example VI Example Aseries of simple tests were studied to demonstrate the ability of otherpairs of immiscible solvents to separate the various isomers ofbenzenehexachloride. The

Employing the column described in Example HI and tests compriseddissolving at room temperature (25 following the same procedure, severalruns were made C. :3" C.) a mixture of 5 grams of gamma isomer andvarying the relative volumes of the respective feed 5 grams of deltaisomer in the pair of solvents, agitating streams. Except for variationin the relative feedvolthe liquid mixture, separating the phases anddetermining umes and operation of the agitating means at 1,000 theweight and isomer content of the solute in each phase. revolutions perminute, the procedure in this example In some instances, the analysis ofthe solute'frommuly duplicated Example 'III. one of two phases wasperformed; the' content-of the other phase may be determined by simpleweight balance.

The results were:

Benzene Isomer content Volume hexa- (percent) Solvent pairs (milllchloride liters) (grams) n-Hexane 300 3. 7 64. 34. Nitromethane. 5O 5. 842. 0 56. 0 n-Hexane 500 4. 5 76. 3 22. 5 Ethylene glycol. 4.00Oyclohexane ethanol.-." Oyclohexane ethanol Cycldhexaua Ethylene glycol.

Ethylene carbonate- Oyclohexane Dimethylformamide CyclohexaneDlmethylformamide 100 Cyelohexane 400 7. 9 56. 0 42. 5 Formamide 75Cyclohexane. 400 7. 6 56.0 41. 5 Furlural 200 Cyelohexane 400 7. 6 56. 041. 5 Formic acid (28%) 200 Cyclohexane 400 6. 1 61. 0 37. 0 Formic acid(88%) 400 3.6 30. 0 68. 0 Cyelohoxane 400 5. 6 58. 0 41. 5 Acetonitrile50 3. 8 41. 5 57. 0 Gyelohexane 400 6. 9 54.0 45. 5 Aniline 100 Alpha:16.5 Beta=0 Gamma=3 6.0 Delta=40.0 Epsilori='5.5'

N The procedure was the same as described in Example V except that 12grams of a mixture having the above composition was employed. Resultswere'as tabulated:

Benzene Isomer content, percent Volume, hexa- Solvent pairmillichloride.

liters weight a B 'y A v e (grams) Benzcne 100 8.1 19. 5' 0.0 40.5 33.06. 5 Ethylene glycoL. 400 3. 6 10. 5 1.0 27. 5 54.5 4. 5Perehloroethylene. 100 5.4 26.0 0.0 53.0 15.5 3.5 Ethylene glycoL- 4006. 3 7.0 1.0 23.0 59." 0 8.0 Ethylene dichlo- I ride 100 4. 9 23. 5 0.047. 0 21. 5 5.0 Ethylene glyool 400 6. 9 13.0 0.5 26. 5 52. 5 6. 0Analysis of feed (12 grams). 16. 5 0.0 36.0 40.0 5. 5

Example VII Employing the apparatus described in Example" III, a solventpair comprising carbon tetrachloride and diethylene glycol was used toextract'the isomers of benzene hexachloride. With this solvent pair, thelight phase, diethylene glycol, was the continuous phase-and the liquidinterface was at the bottom of the column. Carbon tetrachloride wasintroduced via tube 12 into the top of the column, while diethyleneglycol was fed via tube 13 into the lower part of the column.Approximately 3 times as much carbon tetrachloride was'fed as diethylenglycol based on volume.

The isomeric mixture wasintroduced at the center of the column, e.g.,midway between the liquid feed tubes 12 and 13, as a diethylene glycolsolution-containing 50 per cent by weight of benzenehexachloride atbetween 6 0 C. and 80 C. to avoid any crystallization. Between 45 and 50milliliters per hour of this solution was fed during the operation." Thetower temperature, however, was about 25 C. r p

The rate of feed of carbon tetrachloride was such that the efiluentcarbon tetrachloride phase was from 450 to 500 milliliters in volume per45 minutes. Similarly, for 45-minute periods, the diethylene glycolefiluent phase was between 15 3 and 172 milliliters in volume. Thefollowing table indicatesthe observed efiluent volumes for 45-minuteperiods with the operational time indicating the length of time thetower was operating:

. Volume of eflluents, Operation milliliters Sample time,

hours 001 DEG 1 1 Diethylene glycol.

Sample 5 (collection of which started after the tower was in operation 7hours) was analyzed for isomer content in the respective effluent phaseswith these results:

was in Example VII, with the exception that perchloroethylene instead ofcarbon tetrachloride was employed. The volume ratio in this case wasapproximately 2:1, with perchloroethylene being employed in the largervolume. Over a period of 1 /2 hours of operation, the perchloroethyleneefiluent was 200 milliliters and the diethylene glycol effiuent wasbetween 102-105 milliliters for 30 minute eflluent volumes. v

The central feed of diethylene glycol solution of benzene hexachloride(50 percent by weight) was introduced at a rate of 4448 millimeters perhour.

Analysis of a sample of the efiluent streams provided thefollowing'data:

Elhiieiit a 'Y A e 29. U l. 5 58. O 3. 5 5. 5 2- 0 4. 0 1. 0; 76. 0 13.5 21. 0 2. 0 42. 5 20. 5 8. 0

1 Diethylene glycol.

Example IX Stream Milliliters per hour Benzene hexachloride l 22 C C l.4 182-206 Ethylene glycol 550-560 19 The half-hour eflluent pairscollected during the 3% to 4-hour period of operation were analyzed:

20 the continuous phase, the following conditions were used and resultsobtained:

. Eilluent flow, Benzene hexachloride Analysis stream gl fifif 32:?150mm distributmnjpm'cent 5 milliliters per hour Blvlelgneweight,percent,.

liters chloride, chloride grams a a A Perchloro- Dlethweight ethyleneylene (grams) a: B 7 A e 001. 29.5 1.5 50.5 13.0 5.5 glycol Ethyleneglyc O 2.5 2.5 79.0 13.0

d 10 238 1.5 40.0 0.0 27.5 5.5 8.0 324 3.5 22.5 1.5 00.0 5.5 4.0 Feedanalysis 28.2 2.2 55.8 2.4 4.3 When the tower was operated such that theratio of volumes of the efl'luent streams was increased to approxi- AExamples X d X1 ill t th gamma, isomer Itlately 4 t0 1, -8 about foulfillies as much ethylene is selectively distributed in the morepolarsolvent, dis y effiuent as carbon tetrachlorlde efiluent wasleavethylene glycol, whereas the alpha isomer selectively dismg theSystem P 11ml of time, the following results tributes in the less polarsolvent, perchloroethylene. A were Observed: substantial resolution ofthe alpha and gamma isomers is realized in this eleven stage column.With a larger Volume, Benzene Isomer distribution percent number ofstages, e. g., 30 stages, the resolution is more Streammillihexacomplete. I

liters giggl a B 7 A e Optimum resolution of gamma and alpha isomerswith a given solvent pair is facilitated by the relative 2M 00 M volumesof the solvents comprising the pair. These rel- 0.5 4.1 5.0 72.7 15.1ative volumes may differ from those which are used to best advantage inresolving gamma and delta isomers. With a mixture including the alpha,gamma and delta isomers, the relative solvent volumes dictate to a largeExample X extent whether the gamma isomer is selectively distributed orconcentrated in the less polar phase with the Employing the columndescribed in Example III, an alpha isomer, and apart from the deltaisomer, or if it is isomeric benzene hexachloride mixture comprised byinselectively distributed or concentrated in the more polar fra-redanalysis of 33.5 percent alpha, 2.0 percent beta, phase with the deltaisomer and apart from the alpha 48.0 percent gamma, 1.5 percent deltaand 5.5 percent isomer. Examples VIII demonstrate forperchloroethepsilon was fed as a perchloroethylene solution to theylene-diethylene glycol the use of two volumes of percenter of thecolumn. This perchloroethylene solution cnloroethylene per volume ofdiethylene glycol for resowas equivalent to the perchloroethyleneefiluent from a lution of gamma and delta isomers in different solvents.process as described in Example VIII from which per- Example X uses thesolvents in the reverse volume ratio chloroethylene was evaporated togive a benzene hexafor gamma-alpha separation. chloride concentration offifty percent by weight. Di- In conjunction with gamma and alpharesolution, the ethylene glycol was fed into the bottom of the column atvolume ratio of the solvents is frequently of somewhat a rate such thatthe feed volume ratio of perchloroethgreater consequence than withresolution of gamma and ylene to diethylene glycol was 1 to 2. Theconditions delta isomers. The separation coefiicient for gamma and ofoperation and results for a number of operations were: alpha isomers(the ratio of alpha distribution coeflicient Eflluent flow ProductBenzene (milliliters per hour) hexae Sample chloride Run time feed rateBenzene Isomer distribution, percent (minutes) (grams per Perchloro-Diethylene hexahour) ethylene glycol chloride weight (grams) a B 7 A cIn all but run A above, the diethylene glycol phase W COHUHUOUS PhaseIII the column- T Surfer P to gamma distribution coefficient) with manysolvent fi l c 01200 f mmutg pairs is of relatively small magnitude bycomparison 3 is i l 1 S unons W mmute an with other isomer pairs andhence even minor variam n 1 as 'revou ons Per mmu tions in separationcoefiicient are often significant in Example XI facilitating theresolution. Such variation in separation Duplicating Experiment X,except that the perchlorm coefiicient as is experienced with difierentsolvent volume ethylene solution of benzene hexachloride was fed at the1S apparently F l fact that h the two rate of 11.2 grams per hour ofbenzene hexachloride to Phases formed y all lmmlsclble Solvent P111r arep the top of the column, with a stirrer speed of 1200 vorated therespective phases contain minor amounts of the lutions per minute andthe diethylene glycol comprising 7 other solvent of the pair.

This is show-ntby the. following data for the perchlorr:ethylene'diethylene glycol solvent pair:

Data for first two pairs was obtained using 2 grams of gamma and 1 gramalpha; in the last two determinations 3 grams of gamma and 1.5 grams ofalphawere used.

It will be readily realized that according to an embodiment of thepresent invention, resolution of'an isomeric benzene hexachloridemixture including all the isomers, particularly the gamma, alpha anddelta isomers is possible especially by recourse to a plurality ofoperations. In one such procedure, the additive chlorination product ofbenzene (an isomeric benzene hexachloride mixture containing all fiveisomers) may be dissolved in a pair of immiscible solvents of differentpolarity with the consequent formation of two liquid phases, themorepolar solvent predominating in one phase, the less polar solvent inthe other. By appropriately selecting the relative volume of solvents,the selective distribution or concentration of gamma and alpha isomersin the less polar phase is most efficiently achieved; the other isomersincluding the delta isomer selectively distribute or concentrate in themore polar phase. Thus, a bulk separation of gamma and alpha from theother isomers is accomplished.

Resolution of the isomers comprising the solute of the less polar phase(notably the gamma and alpha isomers) may be achieved by dissolving thesolute in a pair of immiscible solvents of ditferent polarity andforming two phases, the less polar solvent predominating in one phaseand the more polar in the other. In this case, by judiciously selectingthe volume ratio of solvents the selective distribution or concentrationof the gamma isomer in the more polar phase is most effectivelyaccomplished. The alpha isomer selectively distributes in the less polarphase.

It is often possible to utitlize directly the less polar phase of thefirst separation in the second stage. The less polar eflluent from afirst stage into which gamma and alpha isomers have been selectivelydistributed may itself comprise one feed stream to a second stagedesigned to resolve gama and alpha isomers. In the event this efiluentis unduly dilute, a portion of the solvent may be removed as byvaporization, and the resulting concentrated solution employed. Or, thesolute may be recovered by removing the solvent and treated with adifferent or fresh immiscible solvent pair.

It will be further understood that the various hereinbefore detailedapparatus and techniques for conducting the resolution of isomers may beemployed in any appropriate combination when recourse is bad tomultistage processes.

Another feature observed in connection with the resolution of alpha andgamma isomers is that impurities which usually may be encountered, e.g.,impurities incident to the manufacture of benzene hexachloride,apparently selectively distribute along with the alpha isomer in theless polar phase. A gamma enriched benzene hexachloride composition ofreduced impurity content, or even free of impurities, thus comprises thesolute of the more polar phase.

This application is a continuation-in-part of application, Serial No.342,348, filed March 16, 1953.

Althouh the invention has been described with reference to certaindetails of specific embodiments, such do tails are not intended toimpose limitations upon the. scope-of the invention, except insofar asthey areincor porated in the' appended claims.v

We claim: 1. A method of preparing a benzene hexachloride compositionwhich comprises dissolving. an isomeric benzenehexachloride mixtureincluding the alpha, gamma and delta isomers in a pair of immisciblesolvents for the benzene hexachloride, said pair comprising a liquidpolyhydricalcohol and a liquid halogenated hydrocarbon, forming twoliquid phases containing dissolved benzene hexachloride, the halogenatedhydrocarbon predominating in one of said phases and the alcoholpredominating in the other, adjusting the relative volumes of the liquidpolyhydric alcohol and liquid halogenated hydrocarbon, selectivelydistributing the gamma and alpha isomers in the halogenated hydrocarbonphase and the delta isomer in the polyhydric alcohol phase, separatingthe .two phases, dissolving the benzene hexachloride isomers of the halogenated hydrocarbon phase and containing less than 4 percent by weightof delta isomer in a second pair of immiscible solvents for benzenehexachloride, said second pair being substantially free of delta isomerand comprising a polyhydric alcohol solvent and a liquid halogenatedhydrocarbon solvent, forming'third and fourth liquid phases containingdissolved benzene hexachloride, the halogenated hydrocarbon solventpredominating in the third phase and the alcohol solvent predominatingin the fourth phase, adjusting the relative volumes of the aliphaticpolyhydric alcohol and halogenated hydrocarbon and selectivelydistributing the gamma isomer in the polyhydric alcohol fourth phase andselectively distributing the alpha isomer in the third phase, andseparating the third and fourth phases, the concentration of gammaisomer in the solute of said fourth phase being greater than the gammaisomer concentration in the benzene hexachloride isomeric mixturedissolved in said second pair of solvents 2. A method of preparing abenzene hexachloride composition which comprises dissolving an isomericbenzene hexachloride mixture including gamma and alpha isomers, saidmixture containing less than 7 percent of delta isomer by weight such asnot to interfere with separation of gamma and alpha isomers, in a pairof immiscible solvents for benzene hexachloride, said pair comprisingliquid polyhydric alcohol and liquid halogenated hydrocarbon, formingtwo liquid phases containing dissolved benzene hexachloride, thehalogenated hydrocarbon predominating in one of said phases and thepolyhydric alcohol predominating in the other, adjusting the relativevolumes of liquid polyhydric alcohol and liquid halogenated hydrocarbon,selectively distributing gamma isomer in the polyhydric alcohol phaseand alpha isomer in the halogenated hydrocarbon phase and separating thetwo phases, the concentration of gamma isomer in the solute of thepolyhydric alcohol phase being greater than the gamma isomerconcentration in said isomeric benzene hexachloride mixture.

3. A method of preparing a benzene hexachloride composition whichcomp-rises dissolving an isomeric benzene hexachloride mixture includingthe alpha, gamma and delta isomers in a pair of immiscible solvents forbenzene hexachloride, said pair comprising liquid polyhydric alcohol andliquid halogenated hydrocarbon, forming two liquid phases containingdissolved benzene hexachloride, the halogenated hydrocarbonpredominating in one of said phases and the alcohol predominating in theother, adjusting the relative volumes of liquid polyhydric alcohol andliquid halogenated hydrocarbon, selectively distributing gamma and alphaisomers in the halogenated hydrocarbon phase and delta isomer in thepolyhydric alcohol phase, separating the two phases, dissolving thebenzene hexachlor-ide isomers of the halogenated hydrocarbon phase andcontaining less than 7 percent by weight of the delta isomer in a secondpair of liquid organic immiscible solvents for benzene hexachloride,said second pair being substantially-free of delta isomer in an amountwhich interferes with the separation of alpha and gamma isomers andcomprising a more polar solvent and a less polar solvent, forming twoimmiscible liquid phases containing dissolved benzene hexachloride, themore polar solvent predominating in one phase and the less polar solventpredominating in the other, selectively distributing gamma isomer in themore polar phase and alpha isomer in the less polar phase, andseparating the two phases, the concentration of gamma isomer in thesolute of the more polar phase being greater than the gamma isomerconcentration in the benzene hexachloride isomeric mixture dissolved insaid second solvent pair.

4. The method of claim 3 wherein the more polar solvent of said secondsolvent pair is selected from the group consisting of normally liquidaliphatic monohydric alcohols, normally liquid polyhydric alcohols andaqueous solutions thereof, and said less polar solvent is selected fromthe group consisting of aliphatic hydrocarbons, cycloaliphatichydrocarbon and halogenated hydrocarbons.

5. A method of preparing a benzene hexachloride composition whichcomprises dissolving an isomeric benzene hexachloride mixture includingthe alpha, gamma and delta isomers in a pair of immiscible solvents forthe benzene hexachloride, said pair comprising glycol and liquidchlorinated hydrocarbon of up to 4 carbon atoms, forming two liquidphases containing dissolved benzene hexachloride, chlorinatedhydrocarbon predominating in one of said phases and glycol predominatingin the other, ad-

jnsting the relative volumes of glycol and liquid chlorinatedhydrocarbon, selectively distributing gamma and alpha isomers in thechlorinated hydrocarbon phase and delta isomer in the glycol phase,separating the two phases, dissolving the benzene hexachlor-ide isomersof the chlorinated hydrocarbon phase and containing less than 7 percentby weight of delta isomer in a second pair of immiscible solvents forbenzene hexachloride, said second pair being substantially free of deltaisomer in an amount which interferes with the separation of alpha andgamma isomers and comprising polyhydric alcohol solvent and liquidhalogenated hydrocarbon solvent, forming third and fourth liquid phasescontaining dissolved benzene hexachloride, the halogenated hydrocarbonsolvent predominating in the third phase and the alcohol solventpredominating in the fourth phase, adjusting the relative volumes ofpolyhydric alcohol and halogenated hydrocarbon and selectivelydistributing gamma isomer in the fourth phase and selectivelydistributing alpha isomer in the third phase, and separating the thirdand fourth phases, the concentration of gamma isomer in the solute ofsaid fourth phase being greater than the gamma isomer concentration inthe benzene hexachloride isomeric mixture dissolved in said second pairof solvents.

References Cited in the file of this patent UNITED STATES PATENTS UNITEDSTATES PATENT QEEICE CERTIFICATE OF 'CORREETION ?atent Nod 2 926, 198February 23 1960 Frederick Ea Kung eta1,

It is hereby certified that error appears in the-printed specificationoi the above numbered patent requiring correction and that the saidLetters Patent should read as corrected below.

Column l line 55, for trichlorobenzen read trichlorobenzene column 8,line 28 for "taht" read that column 9 line 47, for "ther" read tneircolumn 19, line 65 after "was" insert the line 67, for "wer read percolumn .21 line 52, for "gama" read gamma line 74 for "Althouh" readAlthough Signed and sealed this 4th day of April 1961.

(SEAL) Attest:

ERNEST w. SWHDER s; ARTHUR w. CROCKER Officer Acting Commissioner ofPatents Attesting

1. A METHOD OF PREPARING A BENZENE HEXACHLORIDE COMPOSITION WHICHCOMPRISES DISSOLVING AN ISOMERIC BENZENE HEXACHLORIDE MIXTURE INCLUDINGTHE ALPHA, GAMMA AND DELTA ISOMERS IN A PAIR OF IMMISCIBLE SOLVENTS FORTHE BENZENE HEXACHLORIDE, SAID PAIR COMPRISING A LIQUID POLYHYDRICALCOHOL AND A LIQUID HALOGENATED HYDROCARBON, FORMING TWO LIQUID PHASESCONTAINING DISSOLVED BENZENE HEXACHLORIDE, THE HALOGENATED HYDROCARBONPREDOMINATING IN ONE OF SAID PHASES AND THE ALCOHOL PREDOMINATING IN THEOTHER, ADJUSTING THE RELATIVE VOLUMES OF THE LIQUID POLYHYDRIC ALCOHOLAND LIQUID HALOGENATED HYDROCARBON, SELECTIVELY DISTRIBUTING THE GAMMAAND ALPHA ISOMERS IN THE HALOGENATED HYDROCARBON PHASE AND THE DELTAISOMER IN THE POLYHYDRIC ALCOHOL PHASE, SEPARATING THE TWO PHASES,DISSOLVING THE BENZENE, HEXACHLORIDE ISOMERS OF THE HALOGENATEDHYDROCARBON PHASE AND CONTAINING LESS THAN 4 PERCENT BY WEIGHT OF DELTAISOMER IN A SECOND PAIOR OF IMMISCIBLE SOLVENTS FOR BENZENEHEXACHLORIDE, SAID SECOND PAIR BEING SUBSTANTIALLY FREE OF DELTA ISOMERAND COMPRISING A POLYHYDRIC ALCOHOL SOLVENT AND A LIQUID HALOGENATEDHYDROCARBON SOLVENT, FORMING THIRD AND FOURTH LIQUID PHASES CONTAININGDISSOLVED BENZENE HEXACHLORIDE, THE HALOGENATED HYDROCARBON SOLVENTPREDOMINATING IN THE THIRD PHASE AND THE ALCOHOL SOLVENT PREDOMINATINGIN THE FOURTH PHASE, ADJSTING THE RELATIVE VOLUMES OF THE ALIPHATICPOLYHYDRIC ALCOHOL AND HALOGENATED HYDROCARBON AND SELECTIVELYDISTRIBUTING THE GAMMA ISOMER IN THE POLYHYDRIC ALCOHOL FOURTH PHASE ANDSELECTIVELY DISTRIBUTING THE ALPHA ISOMER IN THE THIRD PHASE, ANDSEPARATING THE THIRD AND FOURTH PHASES, THE CONCENTRATION OF GAMMAISOMER IN THE SOLUTE OF SAID FOURTH PHASE BEING GREATER THAN THE GAMMAISOMER CONCENTRATION IN THE BENZENE HEXACHLORIDE ISOMERIC MIXTUREDISSOLVED IN SAID SECOND PAIR OF SOLVENTS.